what would cause my 04 mustang to backfire and want to stall on take off then all of a sudden kick in and sling me down the road . it still starts and runs but wants to hesitate on take off and backfires sometimes it also causes the check engine light to flash when it does this ....i have replaced everything i can think of to fix this other than the fuel pump ....any suggestions?

you should have the engine scanned to see what the engine is turning the light on for. It may be a big clue into what the problem is. Sometimes spark plugs will misfire under load that will cause a problem like this. If you haven't changed the spark plugs in a while the gap will get so big that the ignition spark will look for an easier place to fire. Then the unburned fuel is pushed into the exhaust and a cylinder that did fire normally will ignite the fuel in the exhaust (backfire) Spark plug, coil boot or coil if it's a v8, coil pack, wires or plugs if it's a v6

but scan it first. look for misfire codes. you should look at the mode 6 section for misfires that may not set the check engine light to stay on.

i have changed the spark plugs twice and the wires and coil pack and pvc valve ......i have a diagnostic machine it throws the codes p2197 for the o2 sensor and p0316 ...ive had the issue for a couple months now if i reset the computer it seems to run fine for a day or two then right back to the hesitation on take off and the backfire ...after i reset the computer the check engine light stays off for a while til the problem comes back and when its hesitating the check engine light flashes til what ever is starving it for fuel kicks the fuel out and then send me slinging down the road ....also it doesnt like to sit and idle if its acting fine and i let it idle for more than a few min it makes it start to hesitate to the point of wanting to stall out

I don't understand why you wouldn't say that you knew what codes you had when you made your post. If you have a tool to read the codes do you also have the freeze frame from when the code was set?

every time you reset the computer it goes through a relearn procedure. As soon as the monitors are reset the computer will see the problem that you erased before and will go into limp mode all over again. You have to address the codes not just erase them.

P0316: misfire during the first 1000 rpms after start up.P2197: excessive time between O2 sensor switching or no O2 sensor switching since start up indicates a problem. (always indicates too lean)

things to look at are the ECT, CHT, IAT, MAF, and CKP sensors that are the input for the HO2S monitor. and the CMP and CKP for misfires. Look at the O2 sensors, the fuel trims and see if there is a vacuum leak. Cylinders running too lean will cause a misfire.

What engine does your mustang have? I have had some v6 mustangs that the harmonic balancer bolt has come loose and the balancer moves causing the crank sensor to see the crank shift making it fire at the wrong time.

Sensors in the MAF can get coated with debris that get through the air filter and insulate the sensors making them so they will read lean. Then the engine see less air coming in and give the engine less fuel.

you should also look at mode 6 data. Look for cylinder misfires. there is so much information you can access with a scanner.

You can attach a fuel pressure gauge to the fuel rail and watch what the readings are when you are experiencing the problem. Fuel pressure should be 23-37psi engine running. but if the fuel pressure was the problem why would it only hesitate and then take off? you would think that if it was a fuel pump issue that it would bog and not accelerate because you run out of fuel. But stranger things do happen.